As for leveling guide, I've had much fun with the addon "TourGuide" -- alongside TomTom it works perfectly for my needs and is small and lightweight enough that if I don't choose to use it, it's easy to turn off and forget about. All it does is provide you with a basic leveling guide, to which you can click a little checkbox to skip a step/quest (for example, collections), and it places a arrow on your screen to the next waypoint (i.e. questgivers, mob spawns, etc). You choose the zone, and it's very simple to turn on/off.

For 2 different classes, check out Building Macros for Multiple Roles. Class choices are really a personal preference, so choose whatever you'd like to have based on your goals. For me, I'm an altaholic so I'm leveling up one of everything so I can mix/match at 70. ;)